The problem of high permeability zones which tend to decrease the sweep efficiency of secondary and tertiary oil recovery operations is well known. Various methods are also known for plugging these more permeable zones. For instance, U.S. Pat. No. 3,866,680 discloses injecting a macroemulsion into a formation which tends to flow into the zones of greatest permeability thereby plugging same prior to tertiary recovery operations. However, injection of the macroemulsion involves many problems inherent in forming such a composition above ground. In addition, the material is initially a relatively viscous emulsion which is less capable of penetrating deeply into the formation as compared with the less viscous composition taught in the present process.
Surfactant systems for tertiary oil recovery employing petroleum sulfonate are well known. As a general rule, however, the use of these systems in hard brine connate water is avoided because of the tendency of the divalent ions contained therein to precipitate the sulfonate. For instance, U.S. Pat. No. 3,874,454 discusses this problem.